﻿/*
 * This has been taken over from Josh Smith's MSDN-mag article on MVVM
 * 
 * -> http://msdn.microsoft.com/en-us/magazine/dd419663.aspx
 * 
 */
using System;
using System.Diagnostics;
using System.Windows.Input;

namespace Nova.Studio
{
    /// <summary>
    /// A command whose sole purpose is to relay its functionality to other objects by invoking delegates.
    /// The default return value for the CanExecute method is 'true'.
    /// </summary>
    public class RelayCommand : ICommand
    {
        #region Fields

        protected readonly Action<object>    _execute;
        protected readonly Predicate<object> _canExecute;

        #endregion

        #region Constructors

        /// <summary>
        /// Creates a new command that can always execute.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        public RelayCommand(Action<object> execute)
            : this(execute, null)
        { }

        /// <summary>
        /// Creates a new command.
        /// </summary>
        /// <param name="execute">The execution logic.</param>
        /// <param name="canExecute">The execution status logic.</param>
        public RelayCommand(Action<object> execute, Predicate<object> canExecute)
        {
            if (execute == null)
                throw new ArgumentNullException("execute");

            _execute = execute;
            _canExecute = canExecute;
        }

        #endregion

        #region ICommand Members

        [DebuggerStepThrough]
        public bool CanExecute(object parameter)
        {
            return (_canExecute == null || _canExecute(parameter));
        }

        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }

        public void Execute(object parameter)
        {
            _execute(parameter);
        }

        #endregion
    }
}
